Connect ESP8266 to EPEVER A/B Series ( + MAX485)

Here the material involved:

ESP8266 Dev Board
EPSolar/EPEver Tracer A/B-Series
RS485 UART Module (~~not the MAX485 chip!~~ - @tekk: I'm using MAX485 cheapo module and it works fine!)
An old ethernet cable with RJ45 connector you are happy to cut open

ESP8266 <-> MAX485 module

Required connections:

DI -> D10 / GPIO1 / TX
RO -> D9 / GPIO3 / RX
DE and RE are interconnected with a jumper and then connected to pin D1 / GPIO5
VCC to 3.3V on ESP8266

ESP8266 <-> MAX485 module + SOFTWARE SERIAL (since v3.0.7)

Required connections:

DI -> D2 / GPIO4
RO -> D4 / GPIO2
DE and RE are interconnected with a jumper and then connected to pin D1 / GPIO5
VCC to 3.3V on ESP8266

MAX485 module <-> EPEVER CONTROLLER (RJ45)

Cut open your ethernet cable and split out pin 4, 6, 8 (B, A, GND). Refer to Tracer Modbus PDF for additional info.

Connect wires as follows (make sure your cable matches the color schema below - otherwise refer to pin numbers only):

Ethernet green / pin 6 -> A
Ethernet blue / pin 4 -> B
Ethernet brown / pin 8 -> GND on module and ESP8266 GND pin - -> to prevent ground loops - important!
DON' T use pin 1 or 2 to feed the ESP8266 (they supply 7,5/5V - 50mA maximum)